1. Field of the Invention
This invention relates to power transmission belts and in particular to a rubber compound for use in at least one section of the belt.
2. Description of the Background Art
A number of applications of rubber compounds using silicas and silicates are known. Illustratively, silicas and silicates are utilized in rubber compounds for use as shoe soles and heels wherein the silicas provide stiffness, abrasion resistance, flex resistance, and nonmarking characteristics. Processing rolls utilized in the manufacture of steel, paper and textiles utilize rubber blends having silica therein for toughness and nonmarking characteristics. Off-road tire treads and conveyor belt covers have utilized silica blended rubber to provide cutting and chipping resistance. Skim stocks for tire and belt cords have utilized silicas for adhesion characteristics, and automotive engine mounts have used silicas in the rubber blends for heat resistance. Bumper strips and impact-absorbing devices have used silicas for stiffness, adhesion and desired coloration. Garden hose and cable jackets have utilized silica blended rubber for extrusion, abrasion resistance, and color characteristics.
In connection with the use of silica in the tire blends, increased silica content has been found to lead to a higher index of friction to provide improved stopping distance and starting traction characteristics. One disadvantage in the use of silica in tires has been the relatively high tread wear. In an attempt to reduce such wear, silane coupling agents have been utilized in the formulations.
In power transmission belts, it has been conventional to utilize rubber blends having carbon black in substantial proportion. However, such belts have not proven completely satisfactory because of relatively short life. The need for improvement in durability and reliability of power transmission belts utilizing rubber blends as a component of one or more sections thereof has been manifest. A number of problems have arisen in the use of the conventional carbon black blend rubber belts. Illustratively, cracking has occurred in the adhesion surfaces between the load-carrying cords and the embedding rubber layer known as the cushion layer. This problem has been particularly vexatious relative to the adhesion surfaces adjacent the lower part of the load-carrying cords.
Another problem has arisen in the prior art belts in the cracking in the border layers between the cushion rubber layer embedding the load cords, and the compression rubber layer inwardly thereof.
The problem has been aggravated where the belts have been utilized in environments where the temperature of the belt rises 40 to 90 degrees Centigrade as a result of the heat generated in the running operation.
While the use of ISAF and SAF carbon black have, to some extent, improved the reinforcement of the belt rubber, such reinforcement has not proven fully satisfactory. The need for not only improved cushion rubber strength, but also increased adhesiveness relative to the load-carrying cords and the adjacent belt section materials, has been manifest and continuing. No one heretofore has found a fully satisfactory solution to this vexatious problem.